1. Field of the Invention
The invention relates generally to image projection systems, and particularly to systems for the projection of three-dimensional images.
2. Description of the Related Art
Three-dimensional image displays have long been of interest in a variety of technical applications. Several techniques are known in the prior art for producing three-dimensional images. These techniques include computer graphics which simulate three-dimensional images on a two-dimensional display; stereoscopic displays which mentally fuse two retinal images (left and right) into one image; holographic images which reconstruct the actual wavefront structure reflected from an object; and volumetric displays which create three-dimensional images having real physical height, depth, and width by activating actual light sources within the volume of the display.
U.S. Pat. No. 5,764,317 (the 317 Patent) entitled 3-D Volume Visualization Display describes another technique for generating a three-dimensional image. The 317 Patent employs a volumetric multi-layer screen including a plurality of layers of electrically switchable polymer dispersed liquid crystal (PDLC) film separated by thin transparent dielectric films (or by sheets of glass) coated with transparent electrodes. It is the optical properties of the PDLC that are electrically switchable. Specifically the PDLC film acts as a diffuser when no voltage is applied. Further, under voltage, the film becomes fully transparent. The screen is switchable from a diffusing (scattering) state to a transparent state. Three-dimensional image data is stored in a host computer coupled to the volumetric screen, and the image date is subsequently provided to a liquid crystal television in frame sequences. Each frame is displayed by the liquid crystal television, which has an array of switchable pixels, while light from a lamp passes therethrough to generate a number of cross-sectional images (slices) perpendicular to the direction of viewing. Each image projected by the liquid crystal television is synchronized in time with the activation of one layer of the volumetric screen. By sequentially repeating this process for each image slice (each respective display layer), the observer, it is said, will see a full three-dimensional image within the space encompassing the volumetric screen. If the switching time for the screens is within the range of the persistence of human vision, the consecutively projected slices will be eye integrated into a volumetric image.
The liquid crystal television of the 317 Patent transmits light from the lamp in a pattern formed by switchable pixels in accordance with a frame of image data. Displays in liquid crystal televisions are generally fabricated with microelectronics processing techniques. Each pixel in the display is a region whose transmissive properties can be controlled by an electrical signal. In the liquid crystal television, lamp light incident on a particular pixel is either fully transmitted, partially blocked, or fully blocked by the pixel, depending on the signal applied to that pixel. The transmission of lamp light through any pixel can be varied in steps (gray levels) over a range extending from a state where light is substantially blocked to the state in which incident light is substantially transmitted.
When lamp light is transmitted through the liquid crystal television, the lamp light gains a spatial intensity profile that depends on the transmission state of the pixel array. An image is formed at the liquid crystal television by adjusting the transmission (or gray level) of the pixels to correspond to a desired image.
Holograms may be used to reproduce the effects of a conventional optical element, such as a static lens or a mirror. In certain cases, where complex optical operations are not being reproduced, xe2x80x9cholographic optical elementsxe2x80x9d (HOEs) may be based on simple diffraction gratings. These HOEs may be far easier and less expensive to produce than their glass counterparts, especially when the optical element is complicated or must meet stringent tolerances. HOEs can be compact, lightweight and wavelength-specific, which allows more flexibility in designing optical systems. HOEs may be used to replace individual optical elements, groups of elements, and in some cases, entire systems of conventional optical elements.
Described herein is an apparatus for producing three-dimensional static or moving images. In one embodiment, the apparatus includes an image generator and an optical device. The image generator generates a plurality of image elements including first and second image elements. In one embodiment the image elements constitute coherent beams of light encoded with image information, wherein the coherent beams of light are sequentially generated by one or more laser scanners. The optical device receives the plurality of image elements on a first planar surface thereof and, in response, produces first output light rays and second output rays corresponding to the first and second image elements, respectively. The first and second output light rays, when seen by an observer, appear to originate from first and second common points, respectively, which are spaced from each other in the direction of the observer""s view. In other words, the first and second common points are spaced from each other and from the first planar surface, and the first and second common points are spaced from the first planar surface in a direction perpendicular to the first planar surface. Additionally, mirrors may be employed to enlarge the projected three-dimensional.
In one embodiment, the optical device includes first and second switchable holographic optical elements (SHOEs). The first SHOE is configured to receive the first image element and is switchable between an active state and an inactive state. In the active state, the first SHOE is configured to diffuse the first image element into the first output rays. When operating in the inactive state, the first SHOE is configured to transmit the first image element without substantial alteration. The second SHOE operates similarly to the first SHOE. More particularly, the second SHOE, which is in optical communication with the first SHOE, is configured to receive the second image element and is switchable between an active state and an inactive state. When operating in the active state, the second SHOE is configured to diffuse the second image element into the second output rays. When operating in the inactive state, the second SHOE is configured to transmit the second image element without substantial alteration.
In another embodiment, the optical device includes a light diffuser, a first SHOE and a second SHOE. The light diffuser is configured to sequentially receive and diffuse the first and second image elements into first and second diffused image element components, respectively. The first SHOE is configured to receive first diffused image element components and is switchable between an active state and an inactive state. When operating in the active state the first SHOE is configured to deflect the first diffused image element components into the first output rays. When operating in the inactive state the first SHOE is configured to transmit the first diffused image element components without substantial alteration. The second SHOE is optically positioned between the first SHOE and the light diffuser. The second SHOE is configured to receive components of a second diffused image element components and, similar to the first SHOE, is switchable between an active state and an inactive state. When operating in the active state the second SHOE is configured to deflect the second diffused image element components into deflected second output rays. When operating in the inactive state, the second SHOE is configured to transmit the second diffused image element components without substantial alteration.
In one embodiment, each of the first and second SHOEs are configured to switch between the active and inactive states in less than 150 microseconds. The switching time can be as low as two microseconds.
In one embodiment, the first SHOE includes a holographic recording medium that records a hologram, wherein the holographic recording medium includes a monomer dipentaerythritol hydroxypentaacrylate; a liquid crystal; a cross-linking monomer; a coinitiator; and a photoinitiator dye.
In one embodiment, the first SHOE includes a hologram made by exposing an interference pattern inside a polymer-dispersed liquid crystal material. This polymer-dispersed liquid crystal material includes, before exposure: a polymerizable monomer; a liquid crystal; a cross-linking monomer; a coinitiator; and a photoinitiator dye.
In any embodiment described herein, the image generator can include one or more laser scanners each one of which can produce a coherent light beam encoded with image information. The scanner may scan the coherent light beam over a two-dimensional area such as the planar surface of the optical device.